Rubber process oil is one of the additives for rubber used in rubber manufacture. The rubber process oil is an oil used to improve the plasticity of a rubber or lower the hardness of a vulcanized rubber to improve the processability. It is used properly according to the raw materials of the rubber and the product applications. Ordinarily, aroma-based, naphthene-based, or paraffin-based rubber process oils are used. Since the rubber process oil is required to have compatibility with rubber related to the rubber properties, aroma-based rubber process oils have been usually used for natural rubbers or diene-based synthetic rubbers.
However, since aroma-based rubber process oils usually contain polycyclic aromatics (PCA), the carcinogenic impact on the human body becomes a problem. Handling of mineral oils containing 3 mass % or more of PCA is limited in Europe.
From this background, technologies regarding non-carcinogenic rubber process oil with reduced PCA and good compatibility with rubber have been studied. Technologies relating to naphthene-based rubber process oil (for example, patent documents 1 and 2) and paraffin-based rubber process oil (for example, patent document 3) are disclosed.
However, although the naphthene-based and paraffin-based rubber process oils can reduce the impact on the human body and the environment, they more easily evaporate from the rubber compositions compared to the aroma-based rubber process oil. As a result, the rubber hardness varies as the temperature changes, and heat resistance becomes a problem.